Wired Home Networking.
Most existing offices and some of the newly built buildings facilitate a data network structure based on dedicated wiring. However, implementing such a network in existing buildings typically requires installation of new wiring infrastructure. Such installation of new wiring may be impractical, expensive and problematic. As a result, many technologies (referred to as “no new wires” technologies) have been proposed in order to facilitate a LAN in a building without adding new wiring. Some of these techniques use existing utility wiring installed primarily for other purposes such as telephone, electricity, cable television (CATV), and so forth. Such an approach offers the advantage of being able to install such systems and networks without the additional and often substantial cost of installing separate wiring within the building.
The technical aspect for allowing the wiring to carry both the service (such as telephony, electricity and CATV) and the data communication signal commonly involves using FDM technique (Frequency Division Multiplexing). In such configuration, the service signal and the data communication signals are carried across the respective utility wiring each using a distinct frequency spectrum band. The concept of FDM is known in the art, and provides means of splitting the bandwidth carried by a medium such as wiring. In the case of a telephone wiring carrying both telephony and data communication signals, the frequency spectrum is split into a low-frequency band capable of carrying an analog telephony signal and a high-frequency band capable of carrying data communication or other signals.
A network in a house based on using powerline-based home network is also known in the art. The medium for networking is the in-house power lines, which is used for carrying both the mains power and the data communication signals. A PLC (Power Line Carrier) modem converts a data communication signal (such as Ethernet IEEE802.3) to a signal which can be carried over the power lines, without affecting and being affected by the power signal available over those wires. A consortium named HomePlug Powerline Alliance, Inc. of San Ramon, Calif. USA is active in standardizing powerline technologies. A powerline communication system is described in U.S. Pat. No. 6,243,571 to Bullock et al., which also provides a comprehensive list of prior art publications referring to powerline technology and application. An example of such PLC modem housed as a snap-on module is HomePlug1.0 based Ethernet-to-Powerline Bridge model DHP-100 from D-Link® Systems, Inc. of Irvine, Calif., USA. Outlets with built in PLC modems for use with combined data and power using powerlines are described in US Patent Application 2003/0062990 to Schaeffer et al. entitled ‘Powerline bridge apparatus’. Such power outlets are available as part of PlugLAN™ by Asoka USA Corporation of San Carlos, Calif. USA.
Similarly, carrying data over existing in home CATV coaxial cabling is also known in the art, for example in US Patent application 2002/0166124 to Gurantz et al. An example of home networking over CATV coaxial cables using outlets is described in US Patent application 2002/0194383 to Cohen et al. Such outlets are available as part of HomeRAN™ system from TMT Ltd. of Jerusalem, Israel.
Telephony Definitions and Background
The term “telephony” herein denotes in general any kind of telephone service, including analog and digital service, such as Integrated Services Digital Network (ISDN).
Analog telephony, popularly known as “Plain Old Telephone Service” (“POTS”) has been in existence for over 100 years, and is well-designed and well-engineered for the transmission and switching of voice signals in the 300-3400 Hz portion (or “voice band” or “telephone band”) of the audio spectrum. The familiar POTS network supports real-time, low-latency, high-reliability, moderate-fidelity voice telephony, and is capable of establishing a session between two end-points, each using an analog telephone set.
The terms “telephone”, “telephone set”, and “telephone device” herein denote any apparatus, without limitation, which can connect to a Public Switch Telephone Network (“PSTN”), including apparatus for both analog and digital telephony, non-limiting examples of which are analog telephones, digital telephones, facsimile (“fax”) machines, automatic telephone answering machines, voice (a.k.a. dial-up) modems, and data modems.
The terms “data unit”, “computer” and “personal computer” (“PC”) are used herein interchangeably to include workstations, Personal Digital Assistants (PDA) and other data terminal equipment (DTE) with interfaces for connection to a local area network, as well as any other functional unit of a data station that serves as a data source or a data sink (or both).
In-home telephone service usually employs two or four wires, to which telephone sets are connected via telephone outlets.
Home Networking Existing in-House Wiring.
Similarly to the powerlines and CATV cabling described above, it is often desirable to use existing telephone wiring simultaneously for both telephony and data networking. In this way, establishing a new local area network in a home or other building is simplified, because there is no need to install additional wiring. Using FDM technique to carry video over active residential telephone wiring is disclosed by U.S. Pat. No. 5,010,399 to Goodman et al. and U.S. Pat. No. 5,621,455 to Rogers et al.
Existing products for carrying data digitally over residential telephone wiring concurrently with active telephone service by using FDM commonly uses a technology known as HomePNA (Home Phoneline Networking Alliance) whose phonelines interface has been standardized as ITU-T (ITU Telecommunication Standardization Sector) recommendation G.989.1. The HomePNA technology is described in U.S. Pat. No. 6,069,899 to Foley, U.S. Pat. No. 5,896,443 to Dichter, U.S. Patent application 2002/0019966 to Yagil et al., U.S. Patent application 2003/0139151 to Lifshitz et al. and others. The available bandwidth over the wiring is split into a low-frequency band capable of carrying an analog telephony signal (POTS), and a high-frequency band is allocated for carrying data communication signals. In such FDM based configuration, telephony is not affected, while a data communication capability is provided over existing telephone wiring within a home.
Prior art technologies for using the in-place telephone wiring for data networking are based on single carrier modulation techniques, such as AM (Amplitude Modulation), FM (Frequency Modulation) and PM (Phase Modulation), as well as bit encoding techniques such as QAM (Quadrature Amplitude Modulation) and QPSK (Quadrature Phase Shift Keying) and CCK (Complementary Code Keying). Spread spectrum technologies, to include both DSSS (Direct Sequence Spread Spectrum) and FHSS (Frequency Hopping Spread Spectrum) are known in the art. Spread spectrum commonly employs Multi-Carrier Modulation (MCM) such as OFDM (Orthogonal Frequency Division Multiplexing). OFDM and other spread spectrum are commonly used in wireless communication systems, and in particular in WLAN networks. As explained in the document entitled “IEEE 802.11g Offers Higher Data Rates and Longer Range” to Jim Zyren et al. by Intersil which is incorporated herein by reference, multi-carrier modulation (such as OFDM) is employed in such wireless systems in order to overcome the signal impairment due to multipath. Since OFDM as well as other spread spectrum technologies are considered to be complex and expensive (requiring Digital Signal Processors—DSP), and since telephone wiring is considered a better communication medium wherein multipath is less considered as a major impairment than it is in wireless networks, OFDM technique (and any other spread spectrum or any multi-carrier modulation), which is considered to be powerful and high performance, has not been suggested as a dominant modulation for wired communication in general and over telephone wiring in particular.
There is thus a widely recognized need for, and it would be highly advantageous to have a method and system for using spread spectrum modem technologies such as OFDM for wired applications, such as over utility wiring, and in particular over telephone wiring.
Wireless Home Networking.
A popular approach to home networking (as well as office and enterprise environments) is communication via radio frequency (RF) distribution system that transports RF signals throughout a building to and from data devices. Commonly referred to as Wireless Local Area Network (WLAN), such communication makes use of the Industrial, Scientific and Medical (ISM) frequency spectrum, which is unregulated and license free. In the US, three of the bands within the ISM spectrum are the A band, 902-928 MHz; the B band, 2.4-2.484 GHz (a.k.a. 2.4 GHz); and the C band, 5.725-5.875 GHz (a.k.a. 5 GHz). Overlapping and/or similar bands are used in different regions such as Europe and Japan.
In order to allow interoperability between equipments manufactured by different vendors, few WLAN standards have evolved, as part of the Institute of Electrical and Electronic Engineers (IEEE) 802.11 standard group, branded as WiFi Error! Hyperlink reference not valid. the Wi-Fi Alliance of Austin, Tex., USA. IEEE 802.11b describes a communication using the 2.4 GHz frequency band and supporting communication rate of 11 Mb/s, IEEE 802.11a uses the 5 GHz frequency band to carry 54 MB/s and IEEE 802.11g uses the 2.4 GHz band to support 54 Mb/s. This is described in an Intel White Paper entitled “54 Mbps IEEE 802.11 Wireless LAN at 2.4 GHz”, and a chip-set is described in an Agere Systems White Paper entitled “802.11 Wireless Chip Set Technology White Paper”, both of these documents being incorporated herein by reference.
A node/client with a WLAN interface is commonly referred to as STA (Wireless Station/Wireless client). The STA functionality may be embedded as part of the data unit, or alternatively may be a dedicated unit, referred to as bridge, coupled to the data unit. While STAs may communicate without any additional hardware (ad-hoc mode), such network usually involves Wireless Access Point (a.k.a. WAP or AP) as a mediation device. The WAP implements the Basic Stations Set (BSS) and/or ad-hoc mode based on Independent BSS (IBSS). STA, client, bridge and WAP will be collectively referred to herein as WLAN unit.
Bandwidth allocation for IEEE802.11g wireless in the USA is shown as graph 20 in FIG. 2, along the frequency axis 27. In order to allow multiple communication sessions to take place simultaneously, eleven overlapping channels are defined spaced 5 MHz apart, spanning from 2412 MHz as the center frequency for channel number 1 (shown as 23), via channel 2 centered at 2417 MHz (shown as 24) and 2457 MHz as the center frequency for channel number 10 (shown as 25), up to channel 11 centered at 2462 MHz (shown as 26). Each channel bandwidth is 22 MHz, symmetrically (±11 MHz) located around the center frequency.
WLAN unit block diagram 10 is shown in FIG. 1. For the sake of simplicity, only IEEE802.11g will be described from now on. In general, the wireless physical layer signal is handled in two stages. In the transmission path, first the baseband signal (IF) is generated based on the data to be transmitted, using 256 QAM (Quadrature Amplitude Modulation) based OFDM (Orthogonal Frequency Division Multiplexing) modulation technique, resulting in a 22 MHz (single channel wide) frequency band signal. The signal is then up converted to the 2.4 GHz (RF) and placed in the center frequency of the required channel, and wirelessly transmitted via the antenna. Similarly, the receiving path comprises a received channel in the RF spectrum, down converted to the baseband (IF) from which the data is then extracted.
The WLAN unit 10 connects to the wired medium via port 11, supporting an IEEE802.3 10/100BaseT (Ethernet) interface. The physical layer of this interface is handled by a 10/100BaseT PHY function block 12, converting the incoming Manchester or MLT3 modulated signal (according to the 10BaseT or 100BaseTX coding, respectively) into a serial digital stream. Similarly, a WLAN outgoing digital data stream is modulated to the respective coded signal and transmitted via the port 11, implementing full duplex communication. The internal digital stream may be of proprietary nature of any standard such as MII (Media Independent Interface). Such MII to Ethernet PHY 12 (a.k.a. Ethernet physical layer or Ethernet transceiver) can be implemented based on LAN83C180 10/100 Fast Ethernet PHY Transceiver available from SMSC—Standard Microsystems Corporation of Hauppauge, N.Y. U.S.A. While this function can be implemented by using a single dedicated component, in many embodiments this function is integrated into single component including other functions, such as handling higher layers. The PHY block 12 also comprises the isolation magnetics, balancing, surge protection and connector (commonly RJ-45) required for proper and standard interface via port 11.
For the sake of simplicity, in the foregoing and subsequent description only Ethernet 10/100BaseT interface will be described. However, it will be appreciated that any wired interface, being proprietary or standard, packet or synchronous, serial or parallel may be equally used, such as IEEE1394, USB, PCI, PCMCIA or IEEE1284. Furthermore, multiple such interfaces (being of the same type or mixed) may also be used.
In the case wherein the WLAN unit is integrated and enclosed within another unit (such as data unit, e.g. computer) and does not support a dedicated and direct wired interface, the function of block 12 may be omitted.
MAC (Media Access Control) and higher layers are handled in function block 13, comprising two sub blocks, designated as 10/100BaseT MAC block 13a and IEEE802.11g MAC block 13b (typically, the same MAC device is used for all IEEE802.11 variants, such as a/b/g). The MAC block 13a handles the MAC layer according to IEEE802.3 MAC associated with the wired port 11. Such a function block 13a may be implemented using LAN91C111 10/100 Non-PCI Ethernet Single Chip MAC+PHY available from SMSC—Standard Microsystems Corporation of Hauppauge, N.Y. U.S.A, which includes both the MAC 13a and the PHY 12 functionalities. Reference is made to the manufacturer's data sheet: SMSC—Standard Microsystems Corporation, LAN91C111 10/100 Non-PCI Ethernet Single Chip MAC+PHY, Datasheet Rev. 15 (Feb. 20, 2004), which is incorporated herein by reference. Similarly, the MAC block 13b handles the MAC layer according to IEEE802.11g MAC associated with the wireless port 22. Such MAC 13b is designed to support multiple data rates, encryption algorithms and is commonly based on an embedded processor and various memories. Such a functional block 13b may be implemented using WaveLAN™ WL60040 Multimode Wireless LAN media Access Controller (MAC) from Agere Systems of Allentown, Pa. U.S.A., whose a product brief is incorporated herein by reference, which is part of a full chip-set as described in WaveLAN™ 802.11a/b/g Chip Set document from Agere Systems of Allentown, Pa. U.S.A., which is incorporated herein by reference. Reference is made to the manufacturer's data sheet Agere Systems, WaveLAN™ WL60040 Multimode Wireless LAN Media Access Controller (MAC), Product Brief August 2003 PB03-164WLAN, which is incorporated herein by reference. All the bridging required in order to connect the wired IEEE802.3 MAC handled by block 13a to the wireless IEEE802.11g MAC handled by block 13b is also included in functional block 13, allowing for integrated and proper operation.
The data stream generated by the IEEE802.11g MAC 13b is converted to an OFDM-based baseband signal (and vice versa) by the baseband processor 18. In common applications, the baseband processor 18 (a.k.a. wireless modem and IF transceiver) is implemented by a transmitter/receiver 14 digitally processing the data stream, and an analog unit (I-Q modulator) 15 generating the actual signal. The communication channel in wireless environments imposes various impairments such as attenuation, fading, multi-path, interferences among others, and the transmitter may process the data stream according to the following functions:                a. Packet framing, wherein the data from the MAC 13 is adapted and organized as packets, wherein header, CRC, preamble, control information and end-of-frame delimiter are added.        b. Scrambler.        c. Convolution encoder (such as Viterbi encoder) to allow better robustness against channel impairments such as impulse and burst noise.        d. Puncturer to reduce the required data rate.        e. Interleaver performing permutations on the packet blocks (e.g. bytes) in order to better immune against error bursts by spreading the information.        f. IFFT modulator to produce separate QAM (quadrature Amplitude Modulation) constellation sub-carriers.        
Using digital to analog conversion, the processed digital from the transmitter 14 is used to generate the OFDM baseband signal in the modulator 15. The received OFDM baseband signal from functional block 16 is digitized by the modulator 15, processed by the receiver 14, transferred to MAC 13 and PHY 12 to be conveyed via port 11. Some implementations of WLAN chipsets provide the actual baseband signal, while others provides orthogonal analog I/Q modem signals which need to be further processed to provide the actual real analog form IF (Intermediate Frequency) OFDM baseband signal. In such a case, as known in the art, a Local Oscillator (LO) determining the IF frequency is used to generate a sine wave which is multiplied by the I signal, added to the Q signal multiplied by 90 degrees shifted LO signal, to produce the real analog IF baseband signal. Such function can be implemented based on Maxim MAX2450 3V, Ultra-Low-Power Quadrature Modulator/Demodulator from Maxim Integrated Products of Sunnyvale, Calif. U.S.A, a data sheet of which is incorporated herein by reference. The baseband processor block 18 may be implemented based on WaveLAN™ WL64040 Multimode Wireless LAN Baseband from Agere Systems of Allentown, Pa. U.S.A., whose product brief is incorporated herein by reference. SA5250 Multi-Protocol Baseband from Philips Semiconductors including both baseband processor 18 and MAC 13b functionalities may be alternatively used.
The RF-IF Converter functional block 16 shifts the IF OFDM baseband signal from the IF band to the ISM RF band. For example, an OFDM baseband signal symmetrically centered around 10 MHz and required to use channel 2 centered at 2417 MHz, is required to be frequency shifted by 2417−10=2407 MHz. Such frequency conversion may use many methods known in the art. A direct modulation transmitter/receiver may be used, such as WaveLAN™ WL54040 Dual-Band Wireless LAN Transceiver from Agere Systems of Allentown, Pa. U.S.A., for directly converting the orthogonal I-Q analog signal to the 2.4 GHz RF band. A product brief is incorporated herein by reference. Alternatively, superheterodyne (dual conversion, for example) architecture may be used, as described for SA5251 Multiband RF Transceiver from Philips Semiconductors. The converter 16 and the baseband processor 18 constitute the wireless path physical layer processor 17.
A T/R switch 19 is used to connect the antenna 22 to the transmitter path and disconnect the receiver path (to avoid receiver saturation) only upon a control signal signaling transmission state of the WLAN unit 10. PIN Diode switch based design is commonly used, such as PIN Diode switch SWX-05 from MCE-KDI Integrated Products of Whippany, N.J. U.S.A., whose data sheet is incorporated herein by reference. The antenna 22 is coupled via a RF filter 21 in order to ensure transmitting limited to the defined band mask (removing unwanted residual signals), and to filter out noise and out of band signal in the receiving mode. Such RF filter 21 may use SAW (Surface Acoustic wave) technology, such as 2441.8 MHz SAW Filter from SAWTEK (A TriQuint company) of Orlando, Fla. U.S.A., whose data sheet is incorporated herein by reference.
Actual implementation of the WLAN unit 10 may also involve amplifiers, attenuators, limiters, AGC (Automatic Gain Control) and similar circuits involved with signal level functions. For example, a Low Noise Amplifier (LNA), such as MAX2644 2.4 GHz SiGe, High IP3 Low-Noise Amplifier is commonly connected in the receive path near the antenna 22. Similarly, a Power Amplifier (PA) is used in the transmit path, such as MAX2247 Power Amplifier for IEEE802.11g WLAN. Both the LNA and the PA are available from Maxim Integrated Products of Sunnyvale, Calif. U.S.A. For the sake of simplicity, such functions are omitted in FIG. 1 as well as in the rest of this document. Similarly, wherever either a transmitting or a receiving path is described in this document, it should be understood that the opposite path also exists for configuring the reciprocal path.
Outlets
The term “outlet” herein denotes an electro-mechanical device, which facilitates easy, rapid connection and disconnection of external devices to and from wiring installed within a building. An outlet commonly has a fixed connection to the wiring, and permits the easy connection of external devices as desired, commonly by means of an integrated connector in a faceplate. The outlet is normally mechanically attached to, or mounted in, a wall or similar surface. Non-limiting examples of common outlets include: telephone outlets for connecting telephones and related devices; CATV outlets for connecting television sets, VCR's, and the like; outlets used as part of LAN wiring (a.k.a. structured wiring) and electrical outlets for connecting power to electrical appliances. The term “wall” herein denotes any interior or exterior surface of a building, including, but not limited to, ceilings and floors, in addition to vertical walls.
Wireless Coverage.
Most existing wireless technologies such as IEEE802.11x (e.g. IEEE802.11a/g/b), BlueTooth™, UWB (Ultra WideBand) and others are limited to tens of meters in free line of sight environment. In common building environments, wherein walls and other obstacles are present, the range may be dramatically reduced. As such, in most cases a single wireless unit (such as an access point) cannot efficiently cover the whole premises. In order to improve the coverage, multiple access points (or any other WLAN units) are commonly used, distributed throughout the premises.
In order to allow the access points to interconnect in order to form a single communication cluster in which all the WLAN units can communicate with each other and/or with wired data units, a wired backbone is commonly used, to which the access points are connected. Such a network combining wired and wireless segments is disclosed for example in U.S. Pat. No. 6,330,244 to Swartz et al. Such a configuration is popular today in offices, businesses, enterprises, industrial facilities and other premises having a dedicated wiring network structure, commonly based on Category 5 cabling (a.k.a. structured wiring). The access points interface the existing wiring based on local area network (LAN), commonly by a standard data interface such as Ethernet based 10/100BaseT.
However, installing a dedicated network wiring infrastructure in existing houses is not practical as explained above. The prior art discloses using existing AC power wiring also as the wired backbone for interconnecting WLAN units. Examples of such prior art includes U.S. Pat. No. 6,535,110 to Arora et al., U.S. Pat. No. 6,492,897 to Mowery, Jr., U.S. Patent application 2003/0224728 to Heinonen et al., U.S. Pat. No. 6,653,932 to Beamish et al. Using powerlines as a backbone for connecting WLAN units involves several drawbacks. The type of wiring, noise and the general hostile environment results in a poor and unreliable communication medium, providing low data rates and requiring complex and expensive modems. In addition, the connection of a WLAN unit to the powerline requires both wireless and powerline modems for handling the physical layer over the two media involved, as well as a complex MAC (Media Access control) to bridge and handle the two distinct protocols involved. As such, this solution is complex, expensive and offers low reliability due to the amount of hardware required.
There is thus a widely recognized need for, and it would be highly advantageous to have a method and system for using wireless modem technologies and components in a wired applications. Furthermore, it would be highly advantageous to have a method and system for cost effectively enlarging the coverage of a wireless network by carrying a wireless signal over a wired medium without converting to a dedicated wired modem signal.